Method and device for displaying images of a video sequence

ABSTRACT

A method of displaying images of a video sequence during the spatial navigation in the video sequence in order to pass from a first to a second viewing mode, in which the video sequence comprises encoded images continuously transmitted from a server ( 23 ) to a client machine. The method comprises the following steps, performed by the client machine, during the navigation between the first and second viewing mode: sending to the server at least one request for obtaining supplementary data with respect to images to be displayed (S 205 ) which were received beforehand, and, while awaiting the reception of a response to said at least one request: processing according to the second viewing mode at least one image of current resolution R N  to be displayed (S 203 ), which was received and decoded beforehand, and displaying said at least one processed image (S 204 ).

FIELD OF THE INVENTION

The invention concerns a method and a device for displaying images of avideo sequence during the spatial navigation in the video sequence inorder to pass from a first to a second viewing mode, the video sequencecomprising encoded images continuously transmitted from a server to aclient machine.

The present invention generally concerns the display of images of avideo sequence after their decoding in case of change of viewing mode inthe images of a video sequence and, more particularly, smoothly, rapidlyand without interruption.

A favored but not exclusive application of the present invention that isparticularly worthwhile is the display during the spatial navigation bythe user in the images of the video sequence, such as during operationsof zooming in, zooming out and panning. The display of images from videosequences is further to the transfer of those images in the context of aclient-server architecture, for example in the field of video over theInternet. During operations of spatial navigation, the display mustremain smooth.

BACKGROUND OF THE INVENTION

In this context, the data of the video sequence comprising the encodedimages of the video are transmitted progressively from a remote server,via a network, to a “client” machine, in order to be displayed afterdecoding. This application is relative to “video streaming”applications.

“Video streaming” is a technique which makes it possible to transmit anddisplay a video sequence in real time, i.e. without requiring the priordownloading of a video file before viewing it.

Different systems are known for display of a video sequence duringspatial navigation in the images of that video sequence which istransmitted over a network.

These display systems are dependent on the response speed of thenetwork. Thus, if the performance of the network is reduced, thereactivity of the system is low.

For example, when the user navigates within the images of a videosequence while performing, for example, zooming or panning operations, anavigation request reflecting the user's operation is transmitted to theserver in order for it to be processed.

In response, the server again encodes the data of the images of thevideo sequence to be transmitted to that user, the encoding of theimages of the video sequence having to be made taking into account therequested spatial navigation.

If the performance of the network is poor, the reactivity of the systemis poor, which causes jerky or interrupted display of the re-encodedvideo sequence.

Consequently, according to this technique, in order to produce thespatial navigation requested by the user, the client machine sends arequest for change comprising the parameters of spatial navigation tothe server, the latter performs the recoding of the data of the videoand re-sends the new encoded data to the client machine for them to bedisplayed. In this way, the system is dependent on the lags intransmission of the request and on the transfer time of the result ofthe request that are due to the performance of the network.

The following systems used for performing video streaming are alsoknown: RealOne, Windows Media and Quick Time.

According to these systems, before streaming a video, the video sequenceis encoded beforehand on the server from a video and audio file format,for example MPEG2, MPEG4, DIVX, into a file of format dedicated to videostreaming. After this encoding, the video sequence is sent to one ormore clients.

However, as these video sequences are encoded beforehand, it is nolonger possible to perform the spatial navigation operations in theimages of the video sequence, such as zooming and panning operations,when a video is in course of display.

This is because the video formats used in the aforementioned products donot permit spatial navigation in the video sequence.

Document U.S. Pat. No. 6,698,021 describes, furthermore, a controlsystem for video surveillance cameras using a mechanism of videostreaming.

According to this system, the user remotely controls a surveillancecamera via an Internet browser. A graphical interface enables operationsto be performed of zooming and of panning according to the rotationalaxes of the camera. The instructions from the user are sent to thecamera in order then to be converted into the form of actionscontrolling the zoom of the camera or the motors of the device of thecamera to perform the rotation of the camera about its rotational axes.

The term PTZ (“Pan/Tilt Zoom Camera”) is then employed. Thesesurveillance cameras, of which the zooming and panning operations areperformed electronically, require a costly mechanical system withrespect to a standard camera.

Furthermore, due to its type of operation, the PTZ system is constrainedby the lag time of the network. More particularly, this time isdependent on the sending of the commands requested by the user to thecamera then the reception of the images. Thus, to view a change onscreen, a relatively long time is necessary.

SUMMARY OF THE INVENTION

The present invention aims to mitigate at least one of the aforesaiddrawbacks by providing a method of displaying images of a video sequenceduring the spatial navigation in the video sequence in order to passfrom a first to a second viewing mode, the video sequence comprisingencoded images continuously transmitted from a server to a clientmachine. The method comprises the following steps, performed by theclient machine, during the navigation between the first and secondviewing mode:

-   -   sending to the server at least one request for obtaining        supplementary data with respect to images to be displayed which        were received beforehand,    -   and, while awaiting the reception of a response to said at least        one request:    -   processing according to the second viewing mode at least one        image of current resolution R_(N) to be displayed, which was        received and decoded beforehand, and    -   displaying said at least one processed image.

This displaying method is, in particular, based on the use of the imagesreceived beforehand for the purpose of processing and displaying them,while in parallel or pseudo in parallel sending new requests forsupplementary data with respect to images which were receivedbeforehand.

In this way, on passing from a first to a second viewing mode, theprocessing commences by means of images received beforehand andcontinues with the following images after having received supplementarydata concerning them, enabling the operation desired by the user to beperformed with good visual quality.

Thus, the spatial navigation in a video sequence is performed rapidly,without introducing lag during display, and avoiding interruptions.Moreover, this method permits pleasing viewing of a change of viewingmode by introducing progressive processing of the change in viewingmode.

Furthermore, by contrast to the prior art, this method enables theclient machine to request only the missing data, thus representing a lowvolume of data.

According to a feature, the method further comprises the followingsteps:

-   -   receiving supplementary data in response to said at least one        request, and    -   concatenating the supplementary data received respectively with        the images to be displayed and which were received beforehand.

According to this feature, the received data are concatenatedrespectively with the images received beforehand. On processing of theimages, the supplementary data make it possible to improve the visualrendition during the progressive passage from a first viewing mode to asecond viewing mode.

According to one feature, the selection method comprises the followingsteps:

-   -   decoding encoded images to be displayed comprising supplementary        data of images received in response to an earlier request,    -   processing at least one decoded image according to the second        viewing mode, and    -   displaying said at least one processed image.

Thus, after having received supplementary data, the processing of theimages is performed taking into account the received data, so improvingthe visual rendition during the progressive passage from a first to asecond viewing mode.

According to another feature, the method further comprises the followingsteps:

-   -   storing the encoded images to be displayed in a first memory        (BD) and,    -   storing the corresponding decoded images to be displayed in a        second memory (BI) after their decoding.

In order to rapidly respond to the actions of the user, the method makesit possible to store in a first memory encoded images receivedbeforehand, and in a second memory decoded images received beforehand.More particularly, when an action is made by the user, the processingoperations commence with the images already received and stored, soavoiding an interruption of the display.

According to another feature, the passage from the first to the secondviewing mode is performed on a predetermined batch of images.

According to a first variant embodiment, the spatial navigation consistsof a zoom in.

According to a feature, the sending step comprises:

-   -   sending at least one request for obtaining quality supplementary        data concerning a first batch of encoded contiguous images to be        displayed in the video sequence,    -   sending at least one request for obtaining supplementary data        relative to a higher resolution concerning a second batch of        encoded contiguous images to be displayed, which, in the video        sequence, follows said first batch of encoded contiguous images        to be displayed.

One aspect of this first variant consists of sending at least onerequest for obtaining supplementary data of a quality concerning a firstbatch of images. Those supplementary data concern a small quantity ofdata and enable an enlargement to be made of higher quality.

Another aspect consists of sending at least one request in order toobtain supplementary data relative to a higher resolution concerning asecond batch of images. Those data represent a greater volume of datathan the volume of supplementary data requested earlier. However, theyenable the enlargement requested by the user to be continued giving avery good visual quality.

According to another feature of this variant, at the end of the passagefrom the first to the second viewing mode, the decoded images to bedisplayed are displayed at a higher resolution than the currentresolution.

According to a second variant embodiment, the spatial navigationconsists of a zoom out.

According to a feature, the sending step comprises the sending of atleast one request for obtaining supplementary data concerning the edgesof the encoded images to be displayed which were received beforehand.

This is because the processing of the zoom out operation commences withthe images stored beforehand. However, the edges of the images may bemissing. Thus, a request is sent to the server to obtain the edges ofthe images received beforehand for the purpose of performing a zoom outof good quality.

According to another feature, on passage from the first to the secondviewing mode, the decoded images to be displayed are displayed at alower resolution than the current resolution.

According to one feature of this variant, at the end of the passage fromthe first to the second viewing mode, the decoded images to be displayedare displayed at a lower resolution than the current resolution.

According to another feature, the images of the decoded video sequenceare deleted.

It is probable that the images received beforehand and already decodedand stored in memory BI are narrower than the encoded images stored inmemory BD. Thus, by deleting the images already decoded, the decodingprocessing is again performed on those same images including the edgesnot decoded earlier.

According to a third variant embodiment, the spatial navigation consistsof a pan in the images of the video sequence.

According to a feature of this variant, the sending step comprises thesending of at least one request for obtaining supplementary dataconcerning spatial regions of images to be displayed received beforehandcorresponding to the pan and said spatial regions being located on thepath of the pan.

During a pan, new L-shaped regions are to be displayed. In order to becapable of displaying the content of those L-shaped regions, at leastone request is sent to the server for obtaining the content of theL-shaped regions located on the path of the pan.

According to a feature, the decoding of encoded images to be displayedis carried out at a resolution less than or equal to the currentresolution.

According to a feature of this variant, the images decoded at aresolution less than or equal to the current resolution are extrapolatedto reach the current resolution.

By extrapolating the images of a lower resolution to a higherresolution, a good idea of the content of the image of the new L-shapedregion will be obtained.

According to a feature, the method further comprises a step of modifyingthe decoded images to be displayed by deleting the spatial regions notnecessary for the display and by adding the supplementary data of thedecoded spatial regions.

According to another aspect, the present invention also concerns amethod of displaying images of a video sequence during the spatialnavigation in the video sequence in order to pass from a first to asecond viewing mode, the video sequence comprising encoded imagescontinuously transmitted from a server to a client machine, that areperformed by the client machine. The method comprises the followingsteps:

-   -   sending to the server at least one request for obtaining        supplementary data concerning images to be displayed which were        received beforehand,    -   decoding encoded images comprising supplementary data of images        which were received beforehand in response to said at least one        request,    -   processing according to the second viewing mode at least one        decoded image of current resolution R_(N) to be displayed, and    -   displaying said at least one processed image.

This method has the same advantages as the method of displaying imagesof a video sequence briefly described above and these will therefore notbe reviewed here.

The present invention concerns, furthermore, a device for displayingimages of a video sequence during the spatial navigation in the videosequence in order to pass from a first to a second viewing mode, thevideo sequence comprising encoded images continuously transmitted from aserver to a client machine. The device comprises the following means,adapted to be used by the client machine, during the navigation betweenthe first and second viewing mode:

-   -   means for sending to the server at least one request for        obtaining supplementary data with respect to images to be        displayed which were received beforehand,    -   means for processing according to the second viewing mode at        least one image of current resolution R_(N) to be displayed,        which was received and decoded beforehand, and    -   means for displaying said at least one processed image,    -   said processing and displaying means being activated while        awaiting the reception of a response to said at least one        request.

This device has the same advantages as the method of displaying imagesof a video sequence briefly described above and these will therefore notbe reviewed here.

According to another aspect, the present invention further concerns adevice for displaying images of a video sequence during the spatialnavigation in the video sequence in order to pass from a first to asecond viewing mode, the video sequence comprising encoded imagescontinuously transmitted from a server to a client machine, that areperformed by the client machine, wherein it comprises the followingmeans:

-   -   means for sending to the server at least one request for        obtaining supplementary data concerning images to be displayed        which were received beforehand,    -   means for decoding encoded images comprising supplementary data        of images which were received beforehand in response to said at        least one request,    -   means for processing according to the second viewing mode at        least one decoded image of current resolution R_(N) to be        displayed, and    -   means for displaying said at least one processed image.

This device has the same advantages as the method of displaying imagesof a video sequence briefly described above and these will therefore notbe reviewed here.

According to other aspects, the invention also concerns a computerprogram for an implementation of the methods of the invention describedbriefly above as well as a telecommunication system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general view of a system for viewing a streamed videosequence;

FIG. 2 a shows a general view of a client device for displaying a videosequence according to the invention;

FIG. 2 b is an algorithm of an embodiment of the method of displayingimages of a video sequence during the spatial navigation in the videosequence according to the invention;

FIG. 3 a is a diagrammatic representation of a full resolution digitalimage IM;

FIG. 3 b is a diagrammatic representation of the decomposition of thedigital image IM;

FIG. 4 shows the operations to perform in order to zoom in according tothe invention;

FIG. 5 is an example of a zoom in achieved according to the method ofzooming in of the invention;

FIG. 6 shows the operations to perform in order to zoom out according tothe invention;

FIG. 7 is an example of a zoom out achieved according to the method ofzooming out of the invention;

FIG. 8 is an example of panning within an image;

FIG. 9 shows the operations to perform in order to pan according to theinvention;

FIG. 10 is a diagrammatic representation of an apparatus in which theinvention is implemented.

DETAILED DESCRIPTION

The different aspects of the method and of the device according to theinvention for the display of images of a video sequence in case ofchange of mode of spatial navigation in the video sequence from a firstmode to a second mode of spatial navigation will now be described, byway of example, in the context of their application to the MotionJPEG2000 format. The images may also be sub-images, i.e. parts of imagesof larger format.

For further information concerning the Motion JPEG2000 format, see inparticular the standard ISO/IEC 15444-3.

This method applies principally in the context of a client-serverapplication in which the video data arrive progressively from a remoteserver via a network and are displayed, after being decoded, on a“client” station.

However, other forms of communication may be used.

The Motion JPEG2000 format makes it possible to extract spatial regionsof images of a video sequence at variable resolutions and qualities. Forexample, from a high resolution video, it is possible to view a spatialregion of that video sequence at a lower resolution and with a variablequality.

The communication protocol used between the client and the server makesit possible to exchange the data necessary for performing the display ofthe video sequence, from the server to the client machine.

To do this, the client specifies to the server information for definingthe desired viewing window, in particular the size, the position of theviewing window, the resolution and the quality.

In response to the information from the client, the server provides thecorresponding encoded data of the video sequence.

Similarly, the server may adapt the rate of the images of the videosequence supplied to the client, for example, by supplying only oneimage out of two, or even one image out of three, depending on theclient's request.

The communication protocol called JPIP, which is a standard, wasestablished in order to exchange information and data between a clientand a server. This protocol is particularly well-adapted to the exchangeof data of JPEG2000 or Motion JPEG2000 type.

For further information concerning the JPIP protocol, see in particularthe document entitled “JPEG2000 image coding system—Part 9:Interactivity tools, APIs and protocols—Final Committee Draft”, ISO/IECJTC1/SC29 WG1 N3052, R. Prandolini, S. Houchin, G. Colyer, 25 Jul. 2003.

Other forms of video encoding that have good compression performance,but adopting the same characteristics as Motion JPEG2000, are in courseof study and standardization, in particular MPEG-4 part10, Amendement 1,also termed SVC. The present invention is thus not limited to the MotionJPEG2000 format, but may we widely extended to formats having similarcharacteristics.

FIG. 1 shows a general system for an application of client-server type,which comprises one or more servers 23 in which the video sequences arestored.

The video sequences are stored in a format enabling the transmission ofvideo streams, in particular according to the Motion JPEG2000 format.

They are thus adapted to be loaded and viewed by one or more clientmachines 21.

The client machine contains the means necessary for communicating with aserver via a network 22. The communication protocol used for selectingthe parameters of the video and for transmitting the requests from theuser is, for example, the JPIP protocol. This protocol is particularlywell adapted, in particular for transporting video sequences, in MotionJPEG2000 format.

Furthermore, the client machine comprises a tool for viewing the videosequence, enabling it to perform operations of temporal navigation inthe video sequence, for example, pause, fast forward, and replaying thesequence.

Similarly, the client tool enables operations of spatial navigation tobe performed, in particular by providing the user with options forzooming in, zooming out and panning within the images of the videosequence.

According to this schema, when the user requests a navigation operation,whether it be temporal or spatial, a command is sent from the client tothe server in order to for the latter to respond to the user command.

FIG. 2 a illustrates the different means present in a client machine andFIG. 2 b illustrates the algorithm present in the client machine anddepending on the means of FIG. 2 b for implementing the invention.

The system according to the invention depends on the use of two buffermemories (BD and BI). The first memory BD stores the encoded images ofthe video sequence received from the server for them to be decoded. Thesecond buffer memory BI temporarily stores the decoded images for themto be displayed or for them to be processed prior to them beingdisplayed.

The presence of these two memories will, for a spatial navigationoperation commanded by the user, contribute to rapidly responding to theuser's action user while producing a pleasing graphical rendition, andwithout introducing a lag in the response to the user's command.

More particularly, it is then possible to navigate in the images of thevideo sequence and thus to pass from a first viewing mode to a secondviewing mode in accordance with the commands of the user, whileperforming the operations progressively.

To do this, the system comprises means interaction 30 enabling the userto select a navigation operation. The algorithm of FIG. 2 b commencewith step S201 during which the operation requested by the user isdetected. Next, the algorithm continues by beginning to process imagesalready stored in the buffer memories.

Thus, a batch of encoded images already received is decoded (step S202)using decoding means described below to then be processed according tothe second viewing mode (step S203) by processing means also describedbelow.

The processed images are next displayed (step S204) by displaying meanson the client machine which are, for example, a screen 31.

New requests are also sent to the server in order to requestsupplementary data (step S205). These requests may be sent in parallelto the processing of the stored images. The requests and the processingof the images are indeed carried out in parallel when the hardwarearchitecture is adapted. Otherwise, for example when the hardwarearchitecture is monoprocessor-based, the operating system enablesseveral tasks to be carried out virtually simultaneously, so giving theillusion of parallel processes; the term pseudo parallel is then used.

The new requests are sent to the server, depending on the data necessaryfor achieving the operation selected by the user.

These data concern in particular the size of the viewing window, thespatial region required, the resolution, the frame rate, and the qualityof the images.

The requests also comprise an item of information for identification ofthe images of the sequence on which supplementary data are required.

These requests are produced by means of a request generator 32 whichconverts the navigation operations of the user into JPIP requests.

After processing of the requests by the server 23 of FIG. 1, that serversends the requested data to the client machine.

The responses to the requests of the client machine are received (stepS206) by the JPIP receiver means 33. These responses comprise thesupplementary data, in particular images or portions of images inencoded form.

On reception of these supplementary data, the operations necessary forimplementing the commands of the user will continue progressively withthe use of the images received beforehand and the supplementary data.

These supplementary data are next concatenated respectively with theencoded images received beforehand (step S207) in order to be decoded(S208).

The encoded images of the video sequence which have been received aretemporarily stored in the first buffer memory BD 34 of size MD. The sizeof this buffer memory makes it possible, for example, to store 8 encodedimages.

Decision means 35 enable the sending of the JPIP requests to the serverto be regulated in order for the buffer memory BD to be constantly full.

At step S202, the decoding means 37 (decoder) decode a first batch ofimages received beforehand, while at step S208, those same decodingmeans decode the images received beforehand to which supplementary datahave been concatenated.

The second memory BI 36 will store the decoded images.

Thus, when an encoded image c_(i) is available in memory BD and whenmemory BI comprises at least one free location, image c_(i) may bedecoded by the decoding means 37.

The decoded images are next temporarily stored in the buffer memory BI36. The size MI of that buffer memory BI is, for example, such that itcan store half of the set of the encoded images stored in memory BD,i.e., in the example envisaged, four decoded images.

According to one embodiment, the system is such that the decoded imagesstored in memory BI are kept in memory in buffer memory BD.

Thus, with reference to FIG. 2 a, the encoded image c₁ corresponds tothe encoded data necessary for reconstructing the image i₁. The sameapplies for the following pairs c₂/i₂, c₃/i₃ and c₄/i₄.

The decoding of the images c_(i) by the decoding means 37 is performedfor as long as the buffer memory BI 36 is not filled.

The decoded images contained in the buffer memory BI are ready to beprocessed by the processing means 38. These means perform the necessarygraphical processing operation or operations on the decoded images (stepS203) and display the decoded and processed images on the screen 31(step S204).

The display of the decoded and processed images is carried out at aspecified frame rate, for example 25 images per second.

When an image is loaded into the processing means 38, it is deleted fromthe buffer memory BI 36 and from the buffer memory BD 34, so freeingmemory space for a new image in each memory.

In this way, the display system self-regulates via the two buffermemories BI and BD to correctly display the images at the desired framerate.

The desired frame rate is maintained if the transmission time of thedata for an encoded image between the server and the client device andthe decoding time for an encoded image is faster that the frame rate. Inthe opposite case, the frame rate is not complied with.

The use of a buffer memory BD makes it possible to avoid the problems ofdisplay in case of perturbations in the transmission caused by thenetwork. More particularly, the throughput characteristics of thenetwork often have little constancy over time, or are even veryvariable.

It will be noted that the value of the size MD of the buffer memory BDand the value of the size MI of the buffer memory BI may be variable andmay depend on the hardware capability of the client machine.

The sizes of the buffer memories BD and BI may be re-dimensionedaccording to the characteristics of the network and more particularlythe throughput of that network.

These actions of dimensioning and re-dimensioning are performed by thedecision means 35.

Moreover, decision means 35 may modify certain choices of the user toenable proper and smooth display for the purpose of compensating for thefluctuations in throughput over the network.

Thus, the decision means 35 may, for example, reduce the frame rate orrequest the server to transmit only a few images, or to reduce thequality to reduce the transmission time of the encoded data between twoimages.

FIG. 3 a is a diagrammatic representation of a full resolution digitalimage IM of a video sequence in Motion JPEG2000 format stored on aserver. Each of the images of the video sequence is encoded according toJPEG2000 format.

The JPEG2000 format is a format for encoding each image takenindividually, without any temporal prediction technique. This encodingformat has the advantage of enabling the extraction of spatial sub-partsof each image of the sequence without however decoding the entirety ofthe encoded data of the image.

Each image is divided into a plurality of spatial regions and decomposedinto elementary entities by a spatio-frequential transformation circuitwhich is a dyadic decomposition circuit with several levels ofdecomposition. The transformation circuit may implement one or morespatio-frequential transformations. For example, a wavelettransformation may be used.

A transformation circuit is, in this embodiment, a conventional set offilters, respectively associated with decimators by two, which filterthe image signal in two directions, into high and low spatial frequencysub-band signals. The relationship between a high-pass filter and alow-pass filter is often determined by the conditions for perfectreconstruction of the signal. It is possible for the filters forvertical and horizontal decomposition not to be identical, even thoughin practice this is generally the case. The transformation circuitcomprises, in particular, three successive analysis circuits fordecomposing the image IM into sub-band signals with four decompositionlevels.

Generally, the resolution of a signal is the number of samples per unitlength used for representing that signal. In the case of an imagesignal, the resolution of a sub-band signal is related to the number ofsamples used per unit length for representing that sub-band signalhorizontally and vertically. The resolution depends on the number ofdecompositions made, the decimation factor and the initial imageresolution.

The first analysis circuit receives the digital image signal IM and, inknown manner, delivers as an output four sub-band signals LL₄, LH₄, HL₄and HH₄ with the highest resolution R₄ in the decomposition.

The sub-band signal LL₄ comprises the components or samples of lowfrequency, in both directions, of the image signal. The sub-band signalLH₄ comprises the components of low frequency in a first direction andof high frequency in a second direction. The sub-band signal HL₄comprises the components of high frequency in the first direction andthe components of low frequency in the second direction. Finally, thesub-band signal HH₄ comprises the components of high frequency in bothdirections.

Each sub-band signal is a set of real samples (which could also beintegers) constructed from the original image, which containsinformation corresponding to a respectively vertical, horizontal anddiagonal orientation of the content of the image, in a given frequencyband. Each sub-band signal can be likened to an image.

The sub-band signal LL₄ is analyzed by an analysis circuit similar tothe previous one in order to supply four sub-band signals LL₃, LH₃, HL₃and HH₃ of resolution level R₃.

The sub-band signal LL₃ is analyzed by a similar analysis circuit inorder to supply four sub-band signals LL₂, LH₂, HL₂ and HH₂ ofresolution level R₂.

Each of the sub-band signals of resolution R₂ also corresponds to anorientation in the image.

The sub-band signal LL₂ is analyzed by an analysis circuit similar tothe previous one in order to supply four sub-band signals LL₀ (byconvention), LH₁, HL₁ and HH₁ of resolution level R₁. It will be notedthat the sub-band LL₀ by itself forms the low frequency resolution R₀.

Each of the sub-band signals of resolution R₁ also corresponds to anorientation in the image.

FIG. 3 b represents the image IMD resulting from the spatio-frequentialtransformation applied to the image IM of FIG. 3 a by the transformationcircuit, into ten sub-bands and with five resolution levels: R₀ (LL₀),R₁(LL₂), R₂ (LL₃), R₃ (LL₄), R₄ (original image). The image IMD containsas much information as the original image IM, but the information isdivided according to frequency into four decomposition levels.

Naturally the number of decomposition levels and consequently ofsub-bands can be chosen differently, for example sixteen sub-bands oversix resolution levels, for a bidimensional signal such as an image. Thenumber of sub-bands per resolution level can also be different. Inaddition, it is possible for the decomposition not to be dyadic. Theanalysis and synthesis circuits are adapted to the dimension of thesignal processed.

In FIG. 3 b the samples resulting from the transformation are storedsub-band by sub-band.

It will be noted that each sub-band of the image IMD is partitioned intoblocks of samples.

A precinct comprises the set of the blocks Bi corresponding to the samespatial region or portion of spatial region in a given resolution i.e.in the set of the frequency sub-bands of that resolution.

The transformation circuit may possibly be connected to a quantizationcircuit, which, for example, implements a scalar or vector quantization.

The quantization circuit is connected to an entropy encoding circuit,which performs an entropy encoding, for example a Huffman encoding, oran arithmetic encoding of the data quantized by the quantizationcircuit.

The quantization and entropy encoding circuits are applied independentlyto each block of each sub-band considered.

The encoded image signal thus conveys blocks of samples obtained byencoding of the original samples and which constitute thebitstream—bitstream being the term used below.

When the image signal is in accordance with the JPEG2000 standard, theseblocks of samples are known as codeblocks.

The encoded image signal also comprises a header which includes inparticular the information concerning the size of the image, i.e. itswidth and its height, its position in a frame of reference, as well asthe number of resolutions Rmax of that image.

The size of the spatial regions for each sub-band at a given resolutionis determined by two parameters signaled by markers in the bitstream ofthe image signal in accordance with the JPEG2000 standard.

If it is desired to reconstruct the image of FIG. 3 a with a resolutionimmediately below, it is of no use to transmit the data of resolution 4i.e. the encoded data of the sub-bands LH₄, HL₄ and HH₄. The data oflevel 3 will be eliminated to obtain a resolution that is still lower.

With reference to FIG. 4, the actions performed when the user requests azoom in operation are described.

According to the example considered, the zoom factor is 2.

Thus, FIG. 4 illustrates the different operations carried out in orderto progressively pass from one image i₀ of zoom factor equal to 1 to animage i₈ of zoom factor equal to 2, the image i₀ being either a completeimage, or a sub-image, i.e. a part of another image.

In the particular case of a zoom in by 2, one solution could consist offormulating a request to the server to obtain the encoded data of theresolution immediately above of the images to be displayed, to decodethem and then to display them. However, this solution causes aconsiderable delay which is not acceptable in the applicationsenvisaged.

According to the invention, the display must not freeze while awaitingcomplementary data but must, on the contrary, progressively perform thezoom requested over several images.

Thus, as soon as the zoom in action is detected, a variable R_(N)representing the new display resolution of the images is initialized tothe current resolution R_(A) incremented by 1 (step S41).

Next, the operations illustrated in FIG. 4 are performed in parallelaccording to the availability of the data.

The first operation consists of creating and sending at least onerequest to the server providing the video sequence in order to obtainsupplementary data with respect to images to be displayed which havebeen received beforehand (step S42).

In this connection, as the throughput of the network is unstable, thetransmission of data is the weak point of the architecture. For thisreason, the first operation consists of requesting the server forsupplementary data which are to be transferred.

The supplementary data requested concern data of the quality ofresolution R_(A) which will be provided to complete encoded imagesstored in the buffer memory BD.

For example, these requests concern a batch of contiguous encoded imagesin the video sequence to be displayed, for example, the encoded imagesi₄ and i₅ stored in the memory BD of FIG. 4.

The supplementary data concern quality information representing a lowvolume of data.

These data, at the time of the zoom in operation, enable a good qualityof enlargement to be obtained.

This is because an enlargement performed solely on the basis of the dataof images already stored of resolution R_(A) would result in anunpleasing visual rendition, whereas the quality supplementary dataprovide the information necessary for producing an enlargement of betterquality.

On reception of the quality supplementary data, these are concatenatedrespectively with the encoded images to be displayed that were receivedbeforehand and stored in the buffer memory BD.

The following operation consists of sending at least one new request inorder to obtain supplementary data relative to the higher resolutionR_(N) (step S43).

These requests concern, in particular, a second batch of contiguousencoded images to be displayed which, in the video sequence, follows thefirst batch of contiguous encoded images to be displayed, for example,the encoded images i₆ to i₈ stored in the memory BD of FIG. 2 a.

On reception of the supplementary data concerning data of higherresolution R_(N), they are respectively concatenated with the encodedimages stored in the buffer memory BD.

The following requests sent to the server are those sent when operationis normal. Thus, the object of those requests is to request completeimages of resolution R_(N) concerning the following images of the videosequence (step S44).

After the reception of quality supplementary data concerning a firstbatch of encoded contiguous images in the video sequence to bedisplayed, for example concerning the encoded images i₄ to i₈, thedecoding means 37 commence decoding of those images.

Once the images have been decoded, they will be stored in the buffermemory BI so long as the memory of the buffer memory is not full, whilewaiting for them to be processed and displayed.

However, during the decoding, only the part of the image necessary todisplay, also termed window, is decoded.

This is because it is of no use to decode the entirety of the image,i.e. information not useful for the operations of enlargement orreduction performed by the processing means 38.

Table 1 given below comprises examples of values of decoding windowsizes as well as the decoding resolution for each image.

The size of the window defined for the decoding also corresponds to thefinal size of the image in the buffer memory BI.

At the end of the decoding of the image i₈, the value of the resolutionR_(A) may then take the value of the resolution R_(N).

The decoded images, stored in the buffer memory BI, are next extractedfrom the buffer memory BI in order for them to be processed anddisplayed.

The extraction of a decoded image from the buffer memory BI also leadsto the extraction of the corresponding encoded image from the buffermemory BD.

In parallel with the requests sent by the client machine to the server,during the zoom operation requested by the user, the processing means 38start the processing of the images stored in buffer memory BI in orderfor them to be displayed.

The processing carried out consists of enlarging or reducing the decodedimages according to the resolution of the decoded images.

In the example of a zoom in by a factor of 2, the processing operationsperformed on each of the images i_(x), for a series of images are statedin Table 1 below: TABLE 1 Processing carried out on the images for azoom in by a factor of 2. Size of the decoded Image Resolution windowProcessing/factor Final size i₀ R_(A) 100 × 100 None 100 × 100 i₁ R_(A)88 × 88 Enlargement: r = 1.125 100 × 100 i₂ R_(A) 80 × 80 Enlargement: r= 1.25 100 × 100 i₃ R_(A) 73 × 73 Enlargement: r = 1.375 100 × 100 i₄R_(A) 67 × 67 Enlargement: r = 1.5 100 × 100 i₅ R_(A) 62 × 62Enlargement: r = 1.625 100 × 100 i₆ R_(N) 115 × 115 Reduction: r = 0.875100 × 100 i₇ R_(N) 107 × 107 Reduction: r = 0.9375 100 × 100 i₈ R_(N)100 × 100 None 100 × 100

The operations of enlargement and reduction are considered asinstantaneous and thus do not introduce any additional delay for thedisplay.

According to the invention, the series of operations already described(steps S41 to S44) makes it possible for the graphical processingoperations on the images already stored in the buffer memory BI to bestarted, and then to continue the processing operations on the followingimages after receiving supplementary information.

Moreover, given that the requests sent to the server consist ofrequesting supplementary data of small volume, those data aretransmitted from the server to the client machine rapidly in order thento be concatenated and stored in the buffer memory BD.

It should be noted that the dimensioning of the buffer memories BI andBD, in terms of size, enables a progressive zoom to be performed over agiven number of images, for example from image i₀ to image i₈, withouthowever stopping the display of the video sequence.

It is also possible to modify the number of images over which qualitysupplementary data are requested (step S42) and the number of imagesover which resolution supplementary data are requested (step S43) bypostponing or advancing the change in processing of the images accordingto the images and the characteristics of the network. Thus, in theexample considered in FIG. 4, quality supplementary data are requested(step S42) for the images i₁ to i₅ and resolution supplementary data(step S43) for the images i₆ to i₈. However, the range of images overwhich steps S42 and S43 apply may be modified in order to adapt theprocessing operations to the performance of the communication network.

FIG. 5 shows the graphical rendition of the zoom in, i.e. theprogressive display, during a factor 2 zoom in operation according tothe invention.

The viewing window of size 100×100 is illustrated by means of a squareshown in dotted line.

For simplicity, the central point of the zoom is fixed here at thecenter of the viewing window.

As shown in Table 1 above, image i₀ is the initial image with respect towhich the user requests a zoom in by a factor of 2. This image is ofresolution R_(A), the image i₀ being either a whole image, or asub-image, i.e. a part of an image.

As from the following image, the zoom in operation is initiated.

Thus, image i₁ is decoded at the resolution R_(A) and stored in thememory BI in the format 88×88. The processing means 38 perform anenlargement by a factor of 1.125 in order to obtain a display size ofthe image i₁ of 100×100.

Similarly, the images i₂ and i₃ are respectively decoded in the format80×80 and 73×73 in order then to be stored in the buffer memory BI.These images are of resolution R_(A). Next, these images are enlarged bya factor respectively of 1.25 and 1.375 in order to be displayed at asize of 100×100.

During this processing, the quality supplementary data required from theserver have been received and are concatenated with the respectiveimages in the buffer memory BD, as represented in FIG. 4.

Thus, the following images i₄ and i₅ are decoded at the resolution R_(A)taking into account the supplementary data received. The window fordecoding those images is respectively of size 67×67 and 62×62. Next,these images are enlarged by a factor respectively of 1.5 and 1.625 inorder to be displayed at a size of 100×100.

Similarly, during this processing, the higher resolution supplementarydata required from the server have been received and are concatenatedwith the respective images in the buffer memory BD, as represented inFIG. 4.

Thus, the following images i₆ and i₇ are decoded at the resolution R_(N)by means of the supplementary data received. The decoding window isrespectively of size 115×115 and 107×107. Next, these images are reducedby a factor respectively of 0.875 and 0.9375 in order to be displayed ata size of 100×100.

Finally, image i₈ of resolution R_(N) is decoded and displayed as wellas the following images of the video sequence.

With reference to FIG. 6, a description will be given of the operationsto perform for a factor 2 zoom out operation requested by the user.

In the same way, in order not to suspend the display of the videosequence, the processing operations will be initiated, and at least onerequest is sent to the server in order to request supplementary data.

The processing operations commence with the updating of the variableindicating the resolution of the decoded images. Thus, the newresolution R_(N) takes the value of the current resolution R_(A)decremented by one unit (step S61).

This step is followed by a verification step making it possible todetermine whether the data missing on decoding are present or not in thebuffer memory BD (step S62).

Given that the transmission unit is the elementary entity as describedearlier, it is possible that the data which have been identified asbeing necessary to perform the zoom out operation and corresponding tothe edges of the images, have been transmitted already.

This is because it is possible for the size of the window projected inthe different resolutions not to coincide with the predefined size ofthe elementary entities, since, on transmission of the encoded images,the client machine in general receives more data than the minimum datanecessary for the display.

In FIG. 3 b a window of the image to be displayed is represented whichdoes not coincide with the blocks of each frequency sub-band.

If, at the verification step, it is determined that there are datamissing for the display of the images, at least one request is sent fromthe client machine to the server in order to obtain supplementary dataof resolution R_(N).

These supplementary data concern the edges of the images of a batch ofimages of the video sequence to be displayed and stored in a buffermemory, in particular, in the buffer memory BD.

According to the example, the requests concern the images i₅ to i₈ inorder to enable them to be displayed at the resolution R_(N).

Data may also be missing with respect to the preceding images i₁ to i₄.However, it is assumed that the value of these data is zero. This isbecause, after the zoom out operation, the images i₁ to i₄ are of 50×50format at resolution R_(N). Thus 3 lines and 3 columns of pixels aremissing for image i₁, 7 lines and 7 columns for image i₂, 11 lines and11 columns for image i₃ and 17 lines and 17 columns for image i₄. Thevalue zero is attributed to the missing data. Next, by means ofreconstruction filters, the wavelet transform will smooth those valuesand blur the edges.

The quality of the images at their edges is slightly affected but, asthis region is limited, it is of low perceptibility for the user.

On the other hand, for images i₅ to i₈, since that region becomesincreasingly large, it is necessary to request the missing data (stepS62).

Concerning the images following image i₈, the process of request sendingfor the obtainment of complete data for the region of the image to bedisplayed recommences (step S63).

On processing of the zoom out, a prior operation is executed consistingof emptying the buffer memory BI containing decoded images. Those imageswill be decoded again on the basis of the encoded data of the imagescontained in the buffer memory BD.

Furthermore, the decoding of the encoded images stored in the buffermemory BD is carried out in parallel to the operations already describedconsisting of sending requests to the server in order to obtainsupplementary information.

The decoding is carried out at the resolution R_(N). The size of thewindows for decoding at the resolution R_(N) is given, by way ofexample, in Table 2 shown below.

As illustrated in FIG. 6, the encoded images i₁ to i₄ are, in a firstphase, decoded. As soon as the supplementary data concerning the encodedimages i₅ to i₈ have been received and concatenated respectively withthe encoded images i₅ to i₈ in the buffer memory BD, the decoding ofthese encoded images is carried out.

In principle, the supplementary data requested for a batch of imagesalready stored are received before the decoding of the images precedingthis batch of images in order for the display of the video sequence tobe smooth.

As previously described with reference to the processing of the zoom in,the size of the buffer memories BD and BI is adjusted as closely aspossible by the decision means 35 according to the average throughput ofthe communication network.

After the decoding of the images, they are stored in the buffer memoryBI. Next, those images are extracted in order to be processed anddisplayed by the means 38 and 31.

Table 2 gives an example of processing to be performed on each of theimages i₀ to i₈ of the video sequence in order to perform zoom out by afactor of 2. TABLE 2 Processing carried out on the images for a zoom outby a factor of 2. Size of the decoding Image Resolution windowsProcessing/factor Final size i₀ R_(N) 100 × 100 None 100 × 100 i₁ R_(N)53 × 53 Enlargement: r = 1.875 100 × 100 i₂ R_(N) 57 × 57 Enlargement: r= 1.75 100 × 100 i₃ R_(N) 61 × 61 Enlargement: r = 1.625 100 × 100 i₄R_(N) 67 × 67 Enlargement: r = 1.5 100 × 100 i₅ R_(N) 72 × 72Enlargement: r = 1.375 100 × 100 i₆ R_(N) 80 × 80 Enlargement: r = 1.25100 × 100 i₇ R_(N) 88 × 88 Enlargement: r = 1.125 100 × 100 i₈ R_(N) 100× 100 None 100 × 100

As for the zoom in operation, the invention enables the data storedbeforehand in the buffer memories BI and BD to be exploited to themaximum extent in order to smoothly display the video while performingthe zoom out.

FIG. 7 shows the graphical rendition of the zoom out, i.e. theprogressive display, during a factor 2 zoom out operation according tothe invention.

For simplicity, the central point of the zoom is fixed here at thecenter of the image i₀.

As shown in Table 2, image i₀ is the initial image with respect to whichthe user requests a zoom out by a factor of 2. This image is ofresolution R_(A).

As from the following image, the zoom out operation is initiated.

To do this, the variable identifying the resolution for decoding ismodified by decrementing its value, and also the current resolutionR_(A) is modified in order to identify the new resolution R_(N).

Image i₁ is then decoded at the resolution R_(N) and stored in thememory BI in the format 53×53. The processing means 38 perform anenlargement by a factor of 1.875 in order to obtain a display size ofthe image i₁ of 100×100.

Similarly, the images i₂ to i₄ are respectively decoded in the format57×57, 61×61 and 67×67 in order then to be stored in the buffer memoryBI. These images are of resolution R_(N). Next, these images areenlarged by a factor respectively of 1.75, 1.625 and 1.5 in order to bedisplayed at a size of 100×100.

During that processing, the supplementary data concerning the edges ofthe following images i₅ to i₈ (these images being stored in the buffermemory BD) have been received after a request to the server and areconcatenated with the respective images in the buffer memory BD, asillustrated in FIG. 6.

Next, these images i₅ to i₈ are decoded at resolution R_(N) taking intoaccount the supplementary data received. The window for decoding isrespectively 72×72, 80×80 and 88×88. Next, these images are enlarged bya factor respectively of 1.375 and 1.25 and 1.125 in order to bedisplayed at a size of 100×100.

Finally, image i₈ of size 100×100 and of resolution R_(N) is decoded anddisplayed as well as the following images of the video sequence.

FIG. 8 represents the different views obtained further to a panningoperation, i.e. a spatial displacement in the image.

It is assumed in the example that the images of the video sequencerepresent a fixed scene.

Just after the display of view v₀, the user requests a panning operationin the image by several pixels towards the upper right corner of theimage. The result of the movement requested corresponds to the finalview v₈.

However, in order not to interrupt the video sequence, a progressivedisplay is implemented according to the invention, making it possible toobtain the missing data corresponding to the movement. Thus, during thatprogressive display, the supplementary data are requested in order toobtain the data enabling the display of the new regions further to thepanning.

Thus, the intermediate views (v₁ to v₈) of the progressive display aredisplayed. That display enables a smooth and regular pan between theinitial view v₀ and the final view v₈.

The cross-hatched regions on each of the views in FIG. 8 illustrate thenew spatial region to decode for each image with respect to the initialview v₀ which is the spatial reference.

It should be noted that images i₁ to i₈ stored in the buffer memories BDand BI before the panning operation have the same spatial reference v₀.

With reference to FIG. 9, a description is now given of the differentsteps performed when a panning operation is requested by the user in acurrent resolution R_(N).

The first step consists, for the first images i₁ to i₄, of decoding thedata for the resolutions lower than the current resolution and which arestored in the memory BD, these data however entirely covering the newL-shaped region arising from the pan and represented in FIG. 8.

Given that the L-shaped region is of small size for the images ii to i₄(views v₁ to v₄ in FIG. 8), it is probable that at a resolution R_(L)less than or equal to the current resolution R_(N) the encoded datacorresponding to the L-shaped region have already been transmitted andstored in the memory BD (step S91).

Thus, the two image portions composing the “L” at resolution R_(L) aredecoded.

At the time of the display, the image portions forming the “L” whichhave been decoded at the resolution R_(L) are extrapolated to reach theinitial resolution R_(N).

It is possible that the quality of the image composing the “L” is oflower quality than the rest of the image but the rendition gives quite agood idea of the real content of the offset image.

Thus, as the data are in memory, no supplementary information isrequested for the first images of the video sequence for a panningoperation. On account of that, this makes it possible to rapidly processthe first images following the panning operation without leading tostoppage of the video sequence.

For the following images, for example, the images i₅ to i₈, a request issent to request supplementary data (step S92).

For reasons of speed, only a sub-portion of the missing encoded data maybe requested for the first images i₅ and i₆ and the entirety of theencoded data may be requested for the images i₇ to i₈. That sub-portioncorresponds to the same spatial region, but with a lower level ofquality. This makes it possible to receive data rapidly since the volumeof those data is low. Furthermore, since the requests only aim to obtainsupplementary data, the task of the server is reduced with respect tothe techniques of the prior art.

The following requests sent to the server are those sent when operationis normal. Thus, the object of those requests is to request completeimages (step S93).

The implementation of the policy for obtaining missing encoded datadepends on the reactivity of the network and may be performed by thedecision means 35 of FIG. 2 a.

It is also possible to make that request later if the panning operationis of small magnitude with respect to the viewing window.

In parallel with that first step, the images of memory BI are modified.

This is because, before the panning operation, the decoded imagescontained in the buffer memory BI only contain a sub-portion or even noinformation on the L-shaped portions in the buffer memory BI, arisingfrom the pan.

More particularly, only the portions that are not cross-hatched in FIG.8 are kept in the buffer memory BI, the cross-hatched portionscorresponding to the new portions of the images to be decoded anddisplayed further to a panning operation.

Thus, the decoding means 37 decode the L-shaped portions of each imagewhich are then concatenated respectively with the images already decodedin the memory BI.

Those images are then processed and displayed at the desired frame rate.

In the implementations already described of the operations of zoomingin, zooming out and panning, the buffer memories BD and BI are such thatthe size of the buffer memory BD of the encoded images is twice as greatas the size of the buffer memory BI. However, according to thecapability of the client machine, different memory sizes can beallocated and, for example, may be greater for each of those clientmachines.

The fact of having a high memory size for each of those buffer memoriesensures that the progression of the spatial navigation operations willbe executed rapidly, smoothly and without juddering during the displayin the video sequence.

According to a variant embodiment, the size of the buffer memories mayvary according to the operation of spatial navigation requested by theuser.

With reference to FIG. 10, a description will now be given of a devicewhich has all the means necessary for the implementation of the methodof displaying images of the video sequence according to the invention.

That device is, for example, embedded in a client machine of acommunication network such as the system 21 of the network 22 of FIG. 1.

FIG. 10 represents an information processing device or machine adaptedto operate as a device for displaying images of a video according to theinvention.

According to the embodiment chosen, the device may for example be amicro-computer 1000 connected to different peripherals, for example adigital camera 1001 for the capture of images or any other imageacquisition or storage device, such as a scanner, supplying images tothe computer. These images may be stored in the storage means availableto the micro-computer, such as a hard disk 1002.

The micro-computer 1000 comprises for example a communication interface1003 connected to a communication network 1004, for example the Internetnetwork, and which is adapted to transmit and receive digitalinformation.

The micro-computer 1000 also comprises means for storing data such asthe hard disk 1002, a floppy drive 1005 enabling data to be written ontoa diskette 1006 and that data to be read. The micro-computer may alsocomprise a compact disc reader, not shown (CDROM or DVDROM) on which theimages of the video may be stored, as well as a computer card (PC-CARD)reader, also not shown.

According to a variant, the program or programs enabling device 1000 toimplement the invention are stored on the hard disk 1002.

According to another variant, the executable code or codes of thoseprograms are stored in a ROM (Read Only Memory) 1007 of themicro-computer.

In general terms, an information storage means, which can be read by amicro-computer or microprocessor, whether integrated or not into thatmicro-computer, and which may possibly be removable, is adapted to storea program implementing the method according to the invention

The micro-computer 1000 further comprises a screen 1008 for viewing theimages and a pointing device (not shown), such as a mouse 1009 oroptical stylus, or a keyboard 1010, so as to be able to interact withthe program.

The micro-computer comprises a central processing unit (CPU) 1011, forexample a microprocessor, which controls and directs the execution ofthe instructions of the program or programs relative to the inventionstored in the Read Only Memory ROM 1007 or in the other storage meansdescribed.

The micro-computer 1000 also comprises a Random Access Memory RAM 1012.The RAM may, in particular, comprise registers adapted to store thevariables created and modified during the execution of the program orprograms relative to the invention.

A communication bus 1013 enables communication between the differentelements of the device 1000 and the elements connected thereto.

It will be noted that the representation of the bus 1013 isnon-limiting.

The client machine in which, for example, is embedded the device of FIG.10, may, for example, implement the JPIP protocol (JPEG2000 InternetProtocol).

Of course, the present invention is in no way limited to the embodimentsdescribed and represented, but encompasses, on the contrary, any variantform within the capability of the person skilled in the art.

1. A method of displaying images of a video sequence during the spatialnavigation in the video sequence in order to pass from a first to asecond viewing mode, the video sequence comprising encoded imagescontinuously transmitted from a server (23) to a client machine, whereinit comprises the following steps, performed by the client machine,during the navigation between the first and the second viewing mode:sending to the server at least one request for obtaining supplementarydata with respect to images to be displayed (S205) which were receivedbeforehand, and, while awaiting the reception of a response to said atleast one request: processing according to the second viewing mode atleast one image of current resolution R_(N) to be displayed (S203),which was received and decoded beforehand, and displaying said at leastone processed image (S204).
 2. A method according to claim 1, whereinthe method further comprises the following steps: receivingsupplementary data in response to said at least one request (S206), andconcatenating the supplementary data received respectively with theimages to be displayed and which were received beforehand (S207).
 3. Amethod according to claim 2, wherein the method comprises the followingsteps: decoding encoded images to be displayed comprising supplementarydata of images received in response to an earlier request (S208),processing at least one decoded image according to the second viewingmode (S203), and displaying said at least one processed image (S204). 4.A method according to claim 1, wherein the method further comprises thefollowing steps: storing the encoded images to be displayed in a firstmemory (BD) and, storing the corresponding decoded images to bedisplayed in a second memory (BI) after their decoding.
 5. A methodaccording to claim 1, wherein the passage from the first to the secondviewing mode is performed on a predetermined batch of images.
 6. Amethod according to claim 1, wherein the spatial navigation consists ofa zoom in.
 7. A method according to claim 6, in which the sending stepcomprises: sending at least one request for obtaining qualitysupplementary data concerning a first batch of encoded contiguous imagesto be displayed in the video sequence, sending at least one request forobtaining supplementary data relative to a higher resolution concerninga second batch of encoded contiguous images to be displayed, which, inthe video sequence, follows said first batch of encoded contiguousimages to be displayed.
 8. A method according to claim 6, wherein, atthe end of the passage from the first to the second viewing mode, thedecoded images to be displayed are displayed at a higher resolution thanthe current resolution.
 9. A method according to claim 1, wherein thespatial navigation consists of a zoom out.
 10. A method according toclaim 9, in which the sending step comprises the sending of at least onerequest for obtaining supplementary data concerning the edges of theencoded images to be displayed which were received beforehand.
 11. Amethod according to claim 9, wherein, on passage from the first to thesecond viewing mode, the decoded images to be displayed are displayed ata lower resolution than the current resolution.
 12. A method accordingto claim 9, wherein, at the end of the passage from the first to thesecond viewing mode, the decoded images to be displayed are displayed ata lower resolution than the current resolution.
 13. A method accordingto claim 9, wherein the images of the decoded video sequence aredeleted.
 14. A method according to claim 1, wherein the spatialnavigation consists of a pan in the images of the video sequence.
 15. Amethod according to claim 14, in which the sending step comprises thesending of at least one request for obtaining supplementary dataconcerning spatial regions of images to be displayed received beforehandcorresponding to the pan and said spatial regions being located on thepath of the pan.
 16. A method according to claim 14, characterized inthat the decoding of encoded images to be displayed is carried out at aresolution less than or equal to the current resolution.
 17. A methodaccording to claim 16, wherein said images decoded at a resolution lessthan or equal to the current resolution are extrapolated to reach thecurrent resolution.
 18. A method according to claim 14, wherein themethod further comprises a step of modifying the decoded images to bedisplayed by deleting the spatial regions not necessary for the displayand by adding the supplementary data of the decoded spatial regions. 19.A method of displaying images of a video sequence during the spatialnavigation in the video sequence in order to pass from a first to asecond viewing mode, the video sequence comprising encoded imagescontinuously transmitted from a server to a client machine, that areperformed by the client machine, wherein it comprises the followingsteps: sending to the server at least one request for obtainingsupplementary data concerning images to be displayed which were receivedbeforehand, decoding encoded images comprising supplementary data ofimages which were received beforehand in response to said at least onerequest, processing according to the second viewing mode of at least onedecoded image of current resolution R_(N) to be displayed, anddisplaying said at least one processed image.
 20. A device fordisplaying images of a video sequence during the spatial navigation inthe video sequence in order to pass from a first to a second viewingmode, the video sequence comprising encoded images continuouslytransmitted from a server (23) to a client machine, wherein it comprisesthe following means, adapted to be used by the client machine, duringthe navigation between the first and the second viewing mode: means (32)for sending to the server (23) at least one request for obtainingsupplementary data with respect to images to be displayed which werereceived beforehand, means (38) for processing according to the secondviewing mode of at least one image of current resolution R_(N) to bedisplayed, which was received and decoded beforehand, and means (31) fordisplaying said at least one processed image, said processing anddisplaying means being activated while awaiting the reception of aresponse to said at least one request.
 21. A device according to claim20, wherein the device further comprises: means (33) for receivingsupplementary data in response to said at least one request, and meansfor concatenating the supplementary data received respectively with theimages to be displayed and which were received beforehand.
 22. A deviceaccording to claim 21, wherein the device comprises: means (37) fordecoding encoded images to be displayed comprising supplementary data ofimages received in response to an earlier request, means (38) forprocessing at least one decoded image according to the second viewingmode, and means for displaying said at least one processed image.
 23. Adevice according to claim 20, wherein the device further comprises:means for storing the encoded images to be displayed in a first memory(BD) and, means for storing the corresponding decoded images to bedisplayed in a second memory (BI) after their decoding.
 24. A deviceaccording to claim 20, wherein the spatial navigation consists of a zoomin.
 25. A device according to claim 24, wherein the sending means areadapted to send: at least one request for obtaining qualitysupplementary data concerning a first batch of encoded contiguous imagesto be displayed in the video sequence, and at least one request forobtaining supplementary data relative to a higher resolution concerninga second batch of encoded contiguous images to be displayed, which, inthe video sequence, follows said first batch of encoded contiguousimages to be displayed.
 26. A device according to claim 24, wherein saiddisplaying means are adapted to display the decoded images to bedisplayed at a higher resolution than the current resolution at the endof the passage from the first to the second viewing mode.
 27. A deviceaccording to claim 20, wherein the spatial navigation consists of a zoomout.
 28. A device according to claim 27, in which the sending means areadapted to send at least one request for obtaining supplementary dataconcerning the edges of the encoded images to be displayed which werereceived beforehand.
 29. A device according to claim 27, wherein thedisplaying means are adapted to display the decoded images to bedisplayed at a lower resolution than the current resolution on passagefrom the first to the second viewing mode.
 30. A device according to anyone of claims 27, wherein the displaying means are adapted to displaythe decoded images to be displayed at a lower resolution than thecurrent resolution at the end of the passage from the first to thesecond viewing mode.
 31. A device according to claim 27, wherein thedevice comprises means for deleting the images of the decoded videosequence from the second memory (BI).
 32. A device according to claim20, wherein the spatial navigation consists of a pan in the images ofthe video sequence.
 33. A device according to claim 32, in which thesending means are adapted to send at least one request for obtainingsupplementary data concerning spatial regions of images to be displayedreceived beforehand corresponding to the pan and said spatial regionsbeing located on the path of the pan.
 34. A device according to claim32, wherein the means for decoding encoded images to be displayed areadapted to decode at a resolution less than or equal to the currentresolution.
 35. A device according to claim 34, wherein the devicecomprises means for extrapolating said images decoded at a resolutionless than or equal to the current resolution adapted to extrapolate saidimages to reach the current resolution.
 36. A device according to claim32, wherein the device further comprises means for modifying the decodedimages to be displayed by deleting the spatial regions not necessary forthe display and by adding supplementary data of the decoded spatialregions.
 37. A device for displaying images of a video sequence duringthe spatial navigation in the video sequence in order to pass from afirst to a second viewing mode, the video sequence comprising encodedimages continuously transmitted from a server to a client machine, thatare performed by the client machine, wherein it comprises the followingmeans: means for sending to the server at least one request forobtaining supplementary data concerning images to be displayed whichwere received beforehand, means for decoding encoded images comprisingsupplementary data of images which were received beforehand in responseto said at least one request, means for processing according to thesecond viewing mode of at least one decoded image of current resolutionR_(N) to be displayed, and means for displaying said at least oneprocessed image.
 38. A telecommunication system comprising a pluralityof terminal devices connected via a telecommunication network, whereinit comprises at least one terminal device equipped with a device fordisplaying images of a video sequence according to claim
 20. 39. Acomputer program stored on an information carrier, said programcontaining instructions enabling the implementation of the method ofdisplaying images of a video sequence according to claim 1, when thatprogram is loaded and run by a computer system.